On Relationship between Staircase phenomenon and fatigue. 295 



cells, on the contrary, disengage considerable heat as a result 

 of their Stimulation.^) The products of the activity of the 

 Central Nervous System, therefore, must, for by far the greater 

 part, come from the nerve-cells. 



Among the products of muscular activity are two acids, 

 sarcolactic acid and carbonic acid and we should therefore 

 expect, a priori, if the products of muscular and of nerve-cell 

 activity are similar, to find acid set free in the central nervous 

 System as a result of its activity or fatigue. The Statement 

 is commonly made that this is the case^) and that the acid 

 is lactic acid^), but the evidence does not appear to be of a 

 highly satisfactory nature. The increase in the acidity or 

 hydrogen ion concentration in the brain as a result of prolonged 

 excitation can, however, be readily shown in the following 

 manner: — In a previous paper*) I have pointed out that the 

 sensitiveness of and indicator to changes in hydrogen or hy- 

 droxyl ion concentrations can be greatly augmented by the 

 use of an appropriate solvent immiscible with water. If to 

 10 ccm of a concentrated (2°/o) and very faintly acid Solution 

 of neutral red we add a Single drop of "/^^ KOH the colour 

 of the Solution does not perceptibly change, nevertheless a great 

 change is seen in respect to the lipoid-solubihty of the neutral 

 red if we shake up the original and the faintly alkahne 

 Solutions with Ethyl Acetate. On shaking up with the faintly 

 acid Solution the Ethyl Acetate remains absolutely colourless, 

 while on shaking up with the faintly alkaline Solution the Ethyl 

 Acetata layer is stained deep yellow. In two ways the indi- 

 cator is rendered more sensitive by this method; in the first 

 place a trace of the yellow modification of neutral red, which 

 would be invisible in watery Solution owing to the great excess 

 of the red modification, is removed by the Ethyl Acetate and 



^) Mosso, Croonian Lecture, Phil. Trans. Roy. Soc. London 188, 

 299, 1892. — Arch. Ital. de Biol. 22, 264, 1895. 



2) Heidenhain, Centralbl. f. d. med. Wiss. 1868, 833. — 

 Gscheidlen, Arch. f. d. ges. Physiol. 8, 171, 1874. — Obersteiner, 

 Arch. f. Psychiatrie 29, quoted after the Joum. of Anat. and Physiol. 7, 

 176, 1872. — Moleschott and Battistini, Arch. Ital. de Biol, 8, 

 90, 1887. 



3) Gscheidlen, 1. c. 



*) T. Brailsford Robertson, Journ. of Biol. Chem. 4, 1, 1908. 



